I had my A/C worked on today. I had the switch (used the red one as suggested by GSXR) and the other part replaced that are behind the driver's side head light. He recharged the system and could not get the aux. fan to come on with the A/C on. He let the high side pressure get up to 350 and it still didn't come on. I can jump the fan and make it work, so I know it isn't the fan. What am I missing? What high side pressure activates the fan with the red switch?

I'm sure this has been discussed before, but I couldn't find my situation using the Google search.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

The red switch turns the fan on low speed at 16 bar (232 psi), and turns the fan off at 12 bar (174 psi). Pressures above 300psi should have been way more than enough to trigger the fan (that's even high enough to trigger the old green switch, which needed 290 psi). If you can short the leads of the red switch and make the fan turn on low speed, it sure sounds like a bad switch... bad news is, the system has to be discharged to replace it, then vacuum pulled, and re-charged...




Note: If you are jumping the fan on HIGH speed, using the switch on top of the engine... then check the aux fan resistor. If that's bad, the fan will work on high speed, but not low.



Best regards,

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Thanks Dave. The fan would only come on high when I jumped it at the 100/110 switch. When jumped at the new A/C switch it wouldn't do anything. So I'll keep my fingers crossed that it is the resistor.

Where is the aux fan resistor located? Do I check it for power or......?

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Whew! That's good news - most likely just a bad resistor. It's located near the receiver / drier behind the headlight, below & behind the ABS pump, towards the outside of the car... a real bugger to access. The ABS pump has a black plastic cover, the resistor is pretty much directly below the "S" in "ABS". It's roughly the size of your thumb, it's (dirty) white ceramic with a black metal bracket wrapped around it that may say "Behr" on it.

With the red switch jumped, if you get +12V on one side and nothing on the other, the resistor is bad. Or measure resistance across it, should measure something quite low (say, under 10 ohms)... if it's infinite or very high, it's bad. If you jumper the resistor to bypass it, the fan will run on high when the AC pressure is above 16 bar. This may improve AC performance a bit at low vehicle speeds, the drawback is more noise, a bit more wear on the fan, and increased load on the wimpy stock alternator (especially at night with headlights on).

Can I replace it without moving the ABS unit? Any chance you have a part number handy?

Fortunately it's back to 75 for a high during the day and 45 for the lows at night. So no A/C at night or during the day for that matter.

When I get the 150A alternator I'm getting the 500E headlights so as Sixto put it (my car can serve as a backup lighthouse lamp.) Yes I remember that I'll have to give up my fogs for driving lights.

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Pretty sure it can be done by removing the driver's headlight. I wouldn't mess with the ABS unit. Looks like p/n 000-158-25-45, roughly $25 or so.



Ooooo, nice! Those are kinda spendy now though, plan on ~$750 for a set at current (lousy) exchange rates. Apply Lamin-X film immediately to protect the lenses (the early style lens to 1993 are no longer available, and the 94-95 style lense are ~$300/pair shipped across the pond). With good bulbs, the light output is amazing. Even more amazing with relays & overwatt bulbs...